The transmittance properties of electrochromic materials change in response to electrically driven changes in oxidation state. Thus, when an applied voltage from an external power supply causes electrons to flow to (reduction) or from (oxidation) an electrochromic material, its transmittance properties change. In order to maintain charge neutrality, a charge balancing flow of ions in the electrochromic device is needed. By enabling the required electron and ion flows to occur, an electrochromic device facilitates reversible oxidation and reduction reactions during optical switching.
Conventional electrochromic cells comprise at least one thin film of a persistent electrochromic material, i.e. a material responsive to the application of an electric field of a given polarity to change from a high-transmittance, non-absorbing state to a low-transmittance, absorbing or reflecting state. Since the degree of optical modulation is directly proportional to the current flow induced by an applied voltage, electrochromic devices demonstrate light transmission tunability between high-transmittance and low-transmittance states. In addition, these devices exhibit long-term retention of a chosen optical state, requiring no power consumption to maintain that optical state. Optical switching occurs when an electric field of reversed polarity is applied.
To facilitate the aforementioned ion and electron flows, at least one electrochromic film which is both an ionic and electronic conductor is in ion-conductive contact, preferably direct physical contact, with an ion-conducting material layer. The ion-conducting material may be inorganic or organic, solid, liquid or gel, and is preferably an organic polymer. The electrochromic film(s) and ion-conductive material are disposed between two electrodes, forming a laminated cell. As voltage is applied across the electrodes, ions are conducted through the ion-conducting material.
When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high-transmittance state. Typically, an electrochromic film such as tungsten oxide is deposited on a substrate coated with an electroconductive film such as tin oxide or indium tin oxide to form one electrode. The counter electrode is typically a similar tin oxide or indium tin oxide coated substrate. A complimentary electrochromic film, for example an iridium oxide film, can also be used.
An electrochromic device, such as an electrochromic lens, also requires a means for delivering electrical current from a power source to each of its electrodes. This can be accomplished via use of a bus bar, as disclosed in U.S. Pat. Nos. 5,520,851 and 5,618,390 to Yu, et al.
U.S. Pat. No. 5,471,338 to Yu, et al., discloses the use of a conductive silver epoxy bus bar to make electrical connection to an electrochromic device.
U.S. Pat. No. 3,630,603 to Letter discloses an electrochromic eyewear control circuit. U.S. Pat. No. 4,991,951 to Mizuno discloses metal eyeglass frames used in conjunction with electrooptic lenses.
U.S. Pat. No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin comprising a hydrophilic layer of 2-acrylamido-2-methylpropanesulfonic acid homopolymer and an electrode means for changing electrochromic properties of the device.
U.S. Pat. No. 5,327,281 to Cogan discloses the use of epoxy to seal a cavity formed when a spacer is used to separate electrodes and contains a liquid electrolyte injected between the spaced electrodes.
U.S. Pat. No. 5,657,150 to Kallman, et al., discloses electrochromic devices and the use of contacts connecting first and second electrodes to flex circuits or other means of wiring.